Single channel mobile telephone system



Oct. 28, 1952 R. H. HERRICK 2,616,032.

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l C 6 J 5 Lu N n 5 rr- I0 V N m 1 N IN VEN TOR. ROSWELL H. HE R RICK ATTORNEY Oct. 28, 1952 R. H. HERRICK SINGLE CHANNEL MOBILE TELEPHONE SYSTEM 10v. Sheets-Sheet 3 Filed Oct. 20, 1948 in o INVENTOR ROSWELL H. HERRIOK ATTORNEY Oct. 28, 1952 R. H. HERRICK SINGLE CHANNEL MOBILE TELEPHONE SYSTEM Filed 001:. 20, 1948 10 Sheets-Sheet 4 IO N 9: g INVENTOR.

.NN man now mohomhuo uzo. wm Su r ONN N hm Q3 zoijGwoaooom ROSWELL H HERRICK BY I ATTORNEY Oct. 28, 1952 v HQHERRICK SINGLE CHANNEL MOBILE TELEPHONE SYSTEM Filed Oct. 20, 1948 i0 sheets sheet 5 mubm mmE.

00m Esau Lon INVENTOR. ROSWELL H. HERRIOK ATTOR NEY Oct. 28, 1952 R. H. HERRICK 1 ,532

S'INGLECHANNEL MOBILE .TELEPHONE SYSTEM Filed Oct. 20, 1948 "I Oi' Sh BQ'QSQShBGt-Y TEL DIAL

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MOBILE UNIT 500 Mm RNEY Oct. 28, 1952 R. H. HERRICK $615332 SINGLE CHANNEL-MOBILE TELEPHONE SYSTEM Filed Oct. 20, I948 16 Sheets-sheaf a a: u 2E0 INVENTOR. ROSWELL H. HERRICK ATTORNEY Oct. 28, 1952 R. H. HERRICK SINGLE CHANNEL MOBILE TELEPHONE SYSTEM Filed Oct. 20. 1948 NQE INVENTOR. ROSWELL H. HERRICK BY 7% ATTOR N EY Oct. 28, 1952 R. H. HERRICK SINGLE CHANNELMOBILE TELEPHONE SYSTEM- 10 'SheetS-Sheet-IO Filed Oct. 20, 1948 JNVENTOR.

K m R R E H um L L E w R ATTORNEY v Patented Oct. 28, 1952 SINGLE CHANNEL MOBILE TELEPHONE SYSTEM Roswell H. Herrick, Lorain, Ohio, assignor to Antomatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application October 20, 1948, Serial No. 55,627

23 Claims.

The present invention relates in general to mobile telephone systems, wherein radio transmitters and receivers are employed to complete telephone connections between a fixed station and a number of mobile stations, such as automobiles or pleasure boats or the like, and is particularly concerned with systems of this type for establishing connections between any one of the regular fixed subscribers of a regular land telephone exchange and any one of a group of mobile subscribers, over a single channel.

The main object of the invention is to provide a system of this type which will be operative with a standard automatic telephone exchange, and in which connections may be established in either direction by dialling the regular assigned directory number of the wanted fixed or mobile party, without the intervention of an operator.

Another object of the invention is the incorporation in such a system of complete secret service, with fully selective ringing, and the usual dial-tone, busy-tone, and answer signal, on calls in both directions.

A feature of the invention is the use of two fixed modulating frequencies for each dialling impulse sent over the air, wherein the two frequencies are applied successively to the carrier in a predetermined order and a fixed time relationship, and are held simultaneously on the air for a brief interval before their removal at the end of the first half of each pulse, in order to reduce the danger of interference or false operations from speech frequencies, stray frequencies, static, or other causes.

Another feature consists in the use of only four conductors between the telephone exchange and the fixed radio control station, and the use of these conductors for impulsing, for speech, for tone signals, and for other control functions.

Another feature of the invention is the promatically cuts the mobile unit off the air after an additional interval. This feature prevents any long drawn out conversations which might monopolize the single channel employed. This feature is also effective in case of accident or the like, where a mobile unit might inadvertently or otherwise simulate the initiation of a call.

A further feature consists in the provision of an out-of-range timer in each mobile unit,

whereby, if a mobile subscriber attempts a call 7 with the channel apparently free, and the fixed stations carrier is not received back within a given time interval, the mobile unit is again auto-' matically taken off the air. This feature guards against a mobile subscriber interfering with other calls while out of range of the fixed stations carrier, or while having a defective radio receiver, or the like.

Another feature of the invention is the provision of both amplified and unamplified audible signals and a number of signal lamps in the mobile unit, to advise the mobile subscriber of the condition of the equipment at all times.

Still another feature consists in the provision of a camp-on-busy key in the mobile unit, whereby a mobile subscriber, finding the channel busy on attempting to initiate a call, may by the operation of this key, seize the channel automatically as soon as it is free, and be notified thereof by both visual and audible signals.

Other objects and features of the invention will also be apparent from the specification and claims which follow.

The invention both as to its organization and method of operation together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings comprising Figures 1A, 1B, 10, Figures 2 to 7 inclusive, and Figure 7A which when arranged in accordance with the Figures 8 and 9, illustrate the present invention comprising an automatic exchange I and an associated radio station control circuit 360 which is accessible to the automatic switches in the automatic exchange by means of a trunk repeater circuit 49 and central oflice auxiliary equipment I19. The radio station control circuit 300 cooperates with a group of mobile units, such as the illustrated unit 500.

More particularly, Fig. 1A illustrates in block formation an automatic exchange accessible to a group of subscribers such as T, and the switching apparatus whereby the subscriber T may make or receive calls through the trunk repeater circuit 49.

Figure 1B illustrates the two-way trunk. repeater circuit 49 associated with the automatic exchange whereby incoming and outgoing calls may be automatically extended between the radio station control circuit 300 and the automatic exchange I.

Figure. 1C is a digrammatic illustration of the central office auxiliary equipment I19 which is associated with the trunk repeater in establishing calls between the subscriber in the automatic exchange l and the radio station control circuit 300. 6 Figures 2 and 3 illustrate the details of the radio station control circuit 390 and the apparatus for transmitting and receiving calls to and from the associated mobile units.

Figures 4, 5, 6, 7, and 7A are diagrammatic illustrations of the radio transmitter and receiver equipment located in each of the mobile units, the apparatus in Figure 5 being illustrative of the dash control apparatus in the mobile unit and Figures 4, 6 and 7 being illustrative of the transmitter and receiver and control apparatus located in the mobile unit, with Figure 7A as an alternative to Figure 7.

The automatic exchange is connected to the central ofiice auxiliary equipment I19 by conductors I113, I1I, I12 and I13. The central oifice auxiliary equipment I19 further connects the automatic exchange to the radio station control circuit 350 over conductors I90, I9I, I94 and I95. The outgoing line conductors I91! and IQI from the automatic exchange to the radio station control circuit 389 are connected to the inputcircuit of radio transmitter 35M whereby the connection may be further extended to the mobile units, such as mobile unit 500, by common-channel carrier equipment. A radio receiver 490 in the mobile unit 560 is tuned to the carrier'of transmitter 3M whereby a connection which is established from the automatic exchange may be extended over the radio transmitter 39I and its associated carrier channel to radio receiver 480.

The radio receiver see and the mobile unit control apparatus in turn, extend the call to the telephone handset 50 I. In a similar manner the radio transmitter 690 located in the mobile unit 500 is cooperatively tuned With radio receiver 228 located in the'radio station control circuit 308 whereby the channel associated with this transmitter-receiver pair is utilized to extend a call between the mobile set 50!] and the radio station control circuit 366. The call is further extended by way of the incoming line conductors I94 and I95, to the central ofiice auxiliary equipment I18, trunk repeater circuit 49, and the automatic switching apparatus in the automatic exchange.

Preferably the carrier system comprises a Wellknown commercial type frequency modulated unit wherein the individual-channel carrier transmitter equipment 39I located in the radio station control circuit 39c transmits a given carrier frequency modulated at times with a 3000 cycle and a 2800 cycle tone for signalling purposes. The radio receiver 400 in each mobile unit 500 is tuned tothe carrier frequency of transmitter SGI thereby to comp-rise one of the carrier channels. The individual-channel carrier transmitter 668 located in the mobile unit 508 transmits a diiierent carrier frequency also modulated at times with 3000 and 2800 cycle tones for signalling purposes. Radio receiver 223 in the radio control equipment 300 co-operates with the transmitter 639 to provide a second channel, for calls from the mobile units to the central station.

Considering the drawings in greater detail,

Figure 1A shows subscriber line 2 extending to subscriber sub-station T and a line circuit 1 individually associated with subscriber line 2. The automatic switching apparatus comprises a plurality of groups of finder-selector links, each provided with an associated distributor, and which correspond with the groups of subscriber substations. One of the groups of finder-selector links includes a finder Ii! and the selector I I and is provided with an associated distributor 9 common to the group; which group of finder-selector links is associated with the group of subscriber sub-stations including the'subscriber sub-station T. 1 Also the automatic switching apparatus comprises a plurality of groups of connectors respectively associated with the groups of subscriber sub-stations. One of the groups of connectors includes the connector22 and is associated with a group of subscriber sub-stations including the subscriber sub-station T. The automatic selector link illustrated has access to connector 22 by way of the associated trunk 2 I. Also the selector II has access to the outgoing trunk I2 extending into the trunk repeater circuit 49; while the incoming trunk 28 extending from the trunk repeater circuit 49 is terminated in the incoming selector 24. Finally the incoming selector 2 has access to the connector 22 by way of the associated trunk 2i. Preferably the finders iii, the selectors I I, the selector 24, and the connectors 22, are two motion stepping switches of the well known Strowger type, but not necessarily. It should also be understood that while only one rank 'of selectors is shown, indicating a thousand line office, the insertion of intervening ranks of selectors would readily expand it to a larger size.

Referring to Figure 1B, the trunk repeater circuit 69 there illustrated has a set of leads I4, I5 and I6 comprising trunk I2 which is accessible to selector II. Leads M and I5 are normally connected through the repeater circuit 49 to the talking conductors HI and I12 which extend to the central oifice auxiliary equipment I19. Impulses received over trunk I2 are regenerated by line relay 6% over the signal-out conductor I10 which extends to the central ofiice auxiliary equipment I19. Conductors I1I and I12 serve to transmit the voice frequencies in both directions. The trunk repeater 59 further comprises a signal-in relay III) which is effective to repeat impulses received from a mobile unit over the central oiiice auxiliary equipment I19, to the incoming selector 24 over conductors I1 and I8 of trunk circuit 29. The inward talking circuit associated with the signal-in circuit, passes over the previously mentioned conductors HI and I12 and is further extended over conductors I1 and !8 of trunk 23, and an incoming selector and a connector to the wanted party such as subscriber T. Figure 1C illustrates the central oiiice auxiliary equipment which serves to connect the automatic exchange equipment to the radio station control circuit 330. This equipment is preferably located in the telephone exchange building. If however the location of the telephone exchange is not such as to provide the best radio operating conditions, the fixed radio station equipment may be located at some remote point. The central office auxiliary equipment is connected to the radio station control circuit by two pair of simplexed audio conductors ISil, ISI, I94 and 595. This auxiliary equipment comprises mainly hybrid transformer I83 and an associated balancing network I86. The hybrid transformer I83 serves to eiiect the separation between outgoing and incoming speech, as necessitated by the inherent one-way characteristics of the associated radio transmitter and receiver. The talking conductors Ill and I12 extend-over the midextended to the radio; station. control circuit over conductors I90; and I191; which comprise the outgoing path. The outgoing simplex control con:

ductor- I: likewise extends to the repeating coil:

I;84 and thence over conductors I90 and I91, to the radio station control equipment. Conductors I94 and I95, comprising the incoming audio channel and an. associated simplex circuit are connected to the lower winding of hybrid transformer; I83 whereby the voice currents received over these conductors are induced into the: middle windings of hybrid transformer I83 and. are thereby extended over the conductors HI and I112 to the trunk repeater circuit 49. and tothe automatic exchange. The incoming simplex circuit is extended over conductor I13 to trunk repeater 4.9 for signalling purposes. On outgoing calls, a direct current circuit from the automatic exchange is closed to the radio transmitter control circuit over conductors I10, I90 and I 9I to. seize equipment therein, and the subsequent dial.- lingresults in interruptions of this simplex circuit tooperate relay equipment and more particularly the line relay 200, in the radio station control circuit. Similarly the incoming simplex circuit extending tothe automatic exchange is effective to seize an exchange link, the. incoming impulses being formed by interruptions of the simplex circuit to control the seized. link. In some instances the radio station location will be such that it will be inconvenient orinaccessible to the wire chief and it. is therefore desirable that the radio station control circuit have remotelycontrolled switching circuits. A switch I98 comprising key contacts I39 and I99 is located in the central office auxiliary equipment I19 and is effective when operated tocontrol the master power circuit for the radio station control equipment.

between the central office auxiliary equipment and the radio station control equipment. Indicator light I8] is operated when the remote control operation has been completed.

Figures 2 and 3- illustratethe details of radio station control circuit 300'. Figure 2 showsthe connections between the central office auxiliary equipment I19 and the radio station control circuit 390, which comprise the, outward conductors I80. and I9I, and. the inward conductors I94. and I95. The outward conductors I39- and I9I. are connected to repeating coil 23% whereby the outgoing audio frequencies pass through low pass filter 285-, to conductors 386 and -1 which comprise the input circuit of radio transmitter 391. The simplex circuit associated with the conductors I 90 and ISI is connected from the mid-pointof the primary winding of repeating coil 236- to an outward impulse regenerating system comprising relays 200, 205-, 2E0 and 2,I'5. This relay set is operated responsive to impulses received from the central exchange over-the simplex to operate the radio transmitter 38 I, and, to'connect the output of the dial tone oscillators 289, 290 to the input circuit of the transmitter 30!. The relay arrangement is further effective to repeat the interruptions of the simplex circuit, by converting each impulse into two successive tones of 3000 and 2800 cycles, and superimposing these tones as modulations on the outgoing carrier of radio transmitter 3!.

The radio receiver 228 and its. associated. squelch relay 250 are operated responsive. to.

This remote control function is accomplished over the normal existing conductors receipt: of the carrier. associated. with; the, trans: mitterg-in any'of' the mobile sets, such as the transmitter 600. in. the illustrated. mobile. unit 500. The. radio receiver.- and the squelch. relay on oper.-- ating place: the radio transmitter 30I on the aim, if this has not. been previously accomplished, and: initiate operation of the signal tone detector circuit 29.3. squelch. relay 250 is also operative to, seize the signal-in line relay H0, in the trunk. repeater 49;, over a. simplex arrangement extend1-- ing over the inward conductors I194 and. I95... When the incoming signal frequencies of' 30,001 cycles and 28.00 cycles, modulating thccarrier of" the mobile unit transmitter, pass. from. radioreceiver-228 to the line circuit: 233 and. the input: circuit of. the signal tone detector circuit 293; the tone detector; 293* is thereupon; operated to convert each combination of incoming tones into. a single signal impulse. The inward impulse regenerator system, comprising relays 260,210.. 215 and 280 operates responsive to operation. of; the pulse tone detector circuit 293. to. interrupt the previously completed simplex circuit extend.- ing. over the inward conductors 194 and I95v to;

the central ofilce auxiliary equipment I13 and.

the trunk repeater 49' to control the apparatus. associated therewith. The inward pulse regencrating circuit is of the type illustrated in: the application of Roy W. Jones, Serial No. 694,045,, filed August 30, 1946', Patent No. 2,500,286, granted March 14, 1950'. Complete monitor; supervision is provided-by meansv of;test-jacks 2.2 0, 221:, 222;, 223, 22 i, and 225 whereby the, lines may be tested for line conditions and characteristics. in any direction by means of standardmonitorequipment. Relay 2% is a remotecontrol relay by means of which the attendant using appara: the in the central o-fiiceauxiliary equipment I'I9i may control the power supply for the, radio stationcontrol circuit 300., The outgoing speech frequencies received over conductors. I and H31 are extended as previously mentioned, over the. repeating coil 236 to the low pass filter 285 which has a cut-ofi frequency of approximately 2600 cycles whereby the selected audio frequencies are. then. extended over the conductors 306 and 30-1 to the input circuit of the transmitter 30I, and further to the transmitter modulation circuits located in the radio transmitter. Low pass filter 285 is provided toprevent voice frequencies frominterfering with the dialling circuits. The. radio transmitter 30I is designed to cooperate with. radio receiver 480 in the mobile unit 500 over a. common carrier channel. Likewise the radio. transmitter 680 (Fig. 6) is tuned to a common. channel with radio receiver 223 (Fig. 2) located in the radio station control circuit 3,00. The incoming speech frequencies pass from receiver 223 over line circuit 233, attenuation equalizer 233 and repeating coil 23! to the inward conductors I94 and I95.

Figure 3- illustrates the details of. the power supply panel associated. with the radio station control circuit 300. The power supply panel: includes: a master power switch 323 and. pilot lamp 324 for indicating the position of the master switch. The illustrated stepping on-off." switch; 3I2. including motor magnet 3II and. associated ratchet and cam wheels 3L; and BM is remotely controlled over conductor 399 to energize and; deenergize the power supply panel as required. Pilot lamp 325 indicates the position of the remote control switch. Operation of switch 3.I2 places the radio station control circuit 300 the. stand-by condition. that is the transmitter tube heaters are fully energized, but without anode voltage; and 48 volt direct current is supplied for the operation of the associated relays. Energization of the transformers 302', 328 and 329 by switch 3l2 accomplishes this result. Transmitter control relay 320 is operative from relay 2535 to apply the 115 volt supply at the power panel to transformers 362 and ,321. Transformer 321 and the associated vacuum tube 339 supply the necessary Voltage for placing the tone oscillators 289, 299 and the tone detector 293 in the standby condition. Lamp 3% is operated whenever the high voltage supply circuit is energized, and serves as a warning to the personnel to observe all necessary safety precautions. Switches 333 and 336 test the remote control master switch functions in the radio station control circuit and are normally open.

Figures 4, 5, 6 and 7 illustrate the mobile apparatus, and more specifically, may be divided into dash control apparatus as shown in Figure 5, a transmitter receiver control unit as shown in Figures 4 and 6, and an outof-range and call timer unit, as shown in Figure '7. The dash control apparatus comprises a telephone handset 50I, a switchhook B3 associated with the telephone handset, an impulse dial 5H], a master on-off switch 5H3, a camp-on-busy switch 5l9, and indicating lamps 5M, 5I5, 5H3, and 5H. Lamp 516 is lit whenever the on-off switch is in the operated position. Lamp 5M is illuminated whenever an incoming call is waiting to be answered. The lighting of lamp 5|5 indicates that the mobile set is in use (handset off), while the lighting of lamp 5!? indicates that the mobile unit is beyond the operating range of the associated radio station control units carrier. The dash control apparatus is normally mounted as a unit within easy reach of the operator or driver of the mobile unit, the exact location being of course dependent on the type of vehicle involved. The transmitter-receiver control unit may be mounted in any free space, such as the luggage compartment of the vehicle, for example. The radio receiver 490 is responsive to receipt of the carrier wave from the radio transmitter 3m to operate an associated squelch relay 4), to prepare the mobile transmitter-receiver control circuit and the pulsing tone detector cir- I cuit for operation. The tone detector circuit comprises tubes 403 and 404 and their associated networks M8 and H9. The audio frequency output of the radio receiver 408 is connected to transformer 4|! whereby the received modulation tones are extended to the tone detector circuit.

An impulse regenerating apparatus, connected to and operated by the tone detector, repeats an impulse each time the incoming tones are received in the proper sequence, in the proper timed relation, and in the proper combination of frequencies. This impulse regenerating apparatus comprises relays 440, 445, 450, and 455. A ten-point stepping switch 444, comprising release and motor magnets 458 and 459 and contact banks 464 and 465, is connected to the impulse regencrating arrangement and is operated responsive thereto. Connections to the contact banks464 and 465 are made in such manner that signal relay 410 will be operated only when the switch is operated to each of two predetermined contacts in the banks, in a predetermined sequence. Each mobile unit is given a difierent call number, the arrangement in each unit being such that only the mobile unit having the bank contact connections corresponding to the dialled digits, will be signalled. The connections illustrated in Figure 4 are such that the switch 444 will cause operation of relay 460 responsive to an initial series of four impulses. The illustrated relay 410 will be operated only where the first series of pulses received contains four impulses, and the second series six impulses. Relay 470 is a signalling relay whose operation serves to inform the mobile subscriber of an incoming call.

Figure 6, in addition to the transmitter 600, also includes a power control relay 630, controlled by the hookswitch 593, for starting and stopping a dynamotor 550. The dynamotor 650 is the source of the high voltage supply for the radio transmitter 6%, the said transmitter responding instantly to the application of the high voltage to place the mobile units carrier on the air. The relay 640 is an adapter relay which is arranged, upon operation, to instantly convert the pulse tone detector circuit comprising tubes 403 and 434 and their associated control circuit, into a pulse tone oscillator circuit. The relay BIO and 629 are pulsing relays controlled from the dial 5|!) to connect the signal tones from the tone oscillator circuits to the transmitter input circuit in a predetermined order for dialling over the carrier. Transformer 65L shown in the input circuit of the transmitter 600, is also connected to the handset 59L whereby the speech currents are also conducted to the radio transmitter for transmission purposes.

The timers shown in Figure 7 consist, as previously stated, of an out-of-range timer and a call timer. The out-of-range timer is a bi-metal thermal relay having an operate time of approximately 2 seconds, which is connected so as to operate whenever the mobile unit attempts to initiate a call while outside the operating area of the fixed radio station. This causes the mobile units radio transmitter to be cut off the air, and lights the dash lamp 5|! as notice of the out of range condition. The call timer com prises a motor and reduction gear unit H5, a shaft 125, mounting two cams 129 and 730, and a magnetic clutch H6 for connecting the shaft to the gear reduction unit as required. This timer is arranged to interrupt all incoming or outgoing calls after approximtaely five minutes. It also causes a warning tone to be given to the mobile subscriber after some 4 minutes. This arrangement eliminates the danger of monopoly of the channel by prolonged conversations, or as a result of accidental removal of the telephone receiver from its hook in a mobile unit.

Figure 7A shows the same two timers in a different and alternative form, in which only four standard relays controlled by various timing resistors, having negative temperature coefficients, are employed. In this figure, which may be directly substituted for Figure 7, relays 140, 750, 160 and 110, and the resistors 146, I41, I58, 768, and T14 constitute the call timer, while relay 160 and the resistor 76! serve as the out-ofrange timer.

Placing apparatus in stand-by condition Primarily, the apparatus in the radio station control circuit 300 and the mobile radio sets such as the illustrated set 500 are maintained in a normal stand-by condition while in use. Essentlally, the stand-by condition involves maintenance of the receivers in the fully operative state and the transmitter tube heaters energized, but without anode voltage. Therefore, subsequent aerate n'ergization of the transmitter high voltage supply circuit will instantaneously place the transmitter on the air. Further the stand-by condition requires a direct current battery supply of 48 volts in the grounded positive terminal, for relay operation. In the fixed radio station control circuit 390 the stand-by condition additionally includes energization of the heater supply for the vacuum tubes in the tone oscillator and tone detector circuits 289, 299 and 293 respectively. The first step in preparing the apparatus for use is the closing of the main power supply in the radio station control circuit by means of master power switch 323. Subsequently the remote control master switch 3I2 must be operated whereby the associated contacts 3l5 are closed to supply the necessary power for energizing transformers 302', 328 and 329. The transmitter, the dial tone oscillator and the dial tone detector circuits are thereby placed in the stand-by condition. Operation of masterswitch 3 I2 is accomplished from the central oflice auxiliary equip;-

ment I19 by momentarily operating switch I98 which completes a, loop circuit to relay 249 over the audio frequency lines I94 and I95 extending between the central ofiice auxiliary equipment I19 and the radio station control circuit 390. Assuming the contacts 3 I 5 associated with switch 312 are in the open condition at this time operation of the switch I98 comprising contacts I99, I99 in the central office auxiliary equipment will momentarily disconnect the incoming leads I94 and I95 from the supervisory relay I89 and close a loop circuit extending from exchange battery and ground over resistance I88 and lamp I81, upper contacts of springs I99, and lower contacts of springs I99, conductors I89 and I89, the

lower windings of hybrid coil I83, contacts on test jacks I93 and I91, conductors I94 and I95, contacts on test jacks 22I and 222, primary windings of repeating coil 231, contacts 241 and 249 and through the upper and lower windings of relay 249 and contacts 242. Lamp I81 will not light over this circuit due to the high resistance, but relay 240 operates responsive to completion of the loop circuit, and at its contacts 242 opens the normal series connection between the windings of relay 240, while at its contacts 242 it closes the tip-side of the line to ground through a resistor to light the lamp I81 as an indication to the attendant that the relay 240 has operated. Relay 240 also.- at its contacts 244 opens the normal connection of the simplex circuit extending between the radio station control circuit 300 and the trunk repeater circuit 49, and at its contacts 243 applies battery to the ring side of the line through a protective resistor to further maintain its own circuit. Relay 240 further, at its contacts 24I completes an operating circuit for the motor magnet 3 associated with the on-ofi switch 3I2. Switch 3I2 comprises a motor magnet 3II with anassociated pawl arm, a ratchet cam 3 I3, a cam 3I4 having notched indentations at regular intervals about its outer periphery, a shaft connecting cams 3 I3 and 3I'4, and a microswitch 35I with associated contacts 315. On energization of the motor magnet 3I I, the associated pawl is attracted by the motor magnet to engage a new tooth on the ratchet 3I3. Upon release of the key I98 by the attendant relay 240 restores, and causes the release of the motor magnet 3I I. When the motor magnet 3I I deenergizes the pawl associated therewith is returned to its normal position by a restoring spring353, In returning to its normal position the pawl 352 is forced against the newly engaged tooth on the access thereto, including the connector 22.

ratchet wheel 3I3, which is thereby rotated one step in a clockwise direction, and causes the cam 314 to advance similarly, through the common drive shaft. The outer periphery of cam SM is indented at regularly spaced intervals, each step of the cam causing the high points on the periphery to advance to the positions just vacated by the preceding indentations. Micro-switch 35I comprises a switch arm 354 which is mounted to ride on the outer periphery of cam 3 I4. A small curvature located on the extreme end of this lever alternately engages an indented portion of the cam periphery and a smooth portion of the cam periphery at successive steps of the cam. When the tip of the switch arm is in engagement with an indented portion of the cam periphery, contacts 3I5 associated with micro-switch 35I are in the open position. Assuming the switch is in the open condition, operation of the cam 3I4 one step in a clockwise direction causes the curvature on switch arm 354 to engage a smooth portion of the periphery of cam 3I4 and close contacts 3I5 of micro-switch 35I. A circuit is thereupon completed for energizing transformers 392", 328 and 329 in an obvious circuit from the master power supply. Energization of these transformers supplies the required voltage for placing the radio transmitter 3fll, pulse tone os- -cillator 289-290, and pulse tone detector 293 in a stand-by condition. It is obvious that a subsequent operation of the switch I98 willcause a similar momentary operation of relay 249 and consequent energization and de-energi'zatio'n of motor magnet 3 to cause cams 3I3 and 3 to open contacts 3I5 on microswitch 35I, and to thereby deenergize the radio station control circuit 390.

The mobile set 509 is placed in the stand-by condition by operation of the master switch 5I8 located in the dial panel (Fig. 5) to thereby supply battery potential'to the mobile unit.

Exchange subscriber call to mobile unit A'better understanding of the connections and arrangements of the apparatus incorporated in the illustrated mobile telephone system, as pre-'- viously described, will be facilitated from a con sideration of the extension of connections involving. the automatic exchange I, the radio Station control circuit 300, and the mobile set 590.

Considering, how, the extension of a connedtion between the automatic exchange I and the mobile set 590 and assuming that a call is initiated at the subscriber substation T in the ,au: tomatic exchange I, the line circuit 1 individual to the subscriber line 2 extending to the calling subscriber sub-station T operates in order to place battery potential upon the control conduc= tor 5 of the subscriber line 2, and round po-' tential upon the start conductor 8 extending to the distributor 9 associated with the group of finder selector links, including the link i11us= trated, and comprising the finder I9 and the Be: lector II. p The distributor 9 assigns an-idle link of the finder-selector group mentioned, such, for example, as that illustrated; and initiates op eration of the finder I0 thereof, whereby the finder operates to seize the subscriber line-2 ex tending to the calling subscriber sub-station T. This brings about further operation of the line circuit 1 whereupon ground potential is placed upon the control conductor. 6 of the subscriber line 2 in order to mark the subscriber line 2' as busy to the connectors of the group having Also 11 the line circuit 1 releases the distributor 9 and the selector I I is conditioned to receive the first digit. Dial tone is returned to subscriber T on seizure of the selector to signal the subscriber to proceed with the dialling operation.

Assuming the subscriber at substation T now dials the first digit into the selector I I, to select the radio level, the selector II operates in order to select first, a corresponding group of trunks, and then an idle trunk therein. In this case, since with a Single channel, only one radio call can be made at a time, the selector II will select the outgoing trunk I2 extending to the trunk repeater circuit 49, whereby there is completed a loop circuit extendin from the calling subscriber sub-station T to the line relay 60 in the repeater circuit 69, While the control conductor I6 of the selector II is also extended to the repeater 43, for a purpose more fully explained hereinafter. It is noted that the outgoing trunk I2 is normally marked as idle to the selector II by the application of battery potential thereon through impedance 15, over a path including the contacts 91 and IE5, and control conductor I6. The loop circuit mentioned, extends from ground by way of the lower Winding of line relay 68 and contacts 52 to the line conductor Id of the outgoing trunk I2, and from battery by way of the upper winding of line relay 6!! and contacts to the line conductor I5 of the outgoing trunk I2, and then by way of trunk I2, the selector II and finder I6, and the subscriber line 2 to the calling subscriber substation T.

When this loop circuit is thus completed, the line relay 60 operates to complete at the contacts BI a path for applying ground potential by way of resistor I11 to the signal-out conductor I'IIJ extending to the central ofiice auxiliary equipment I19 and further to the radio station control circuit etc, in order to bring about the operation of the pulsing relay 20!! therein in a manner to be described more fully hereinafter. Also the line relay 65) interrupts at the contacts 62 a termination circuit which includes resistor I14, condenser I15 and extends over contacts I (II, 62 across the line conductors HI and I12 extending between the trunk repeater circuit 33 and the central oflice auxiliary equipment I19. Further, the line relay 60 completes at the contacts 63, an obvious circuit for operating the hold relay I653. Upon operating, the hold relay I60 interrupts, at the contacts I65, the previously traced path for applying battery potential by way of impedance 16 to the control conductor l6 of the outgoing trunk I2, and completes at the contact I66 a path for applying ground potential to the control conductor I6 of the outgoing trunk I2. Ground potential applied to the control conductor I6 of the outgoing trunk I2 marks the outgoing trunk I2 as busy to the other selectors. The signal-out circuit from line relay 60 extends from ground over resistance I11. through contacts BI, over the signal-out conductor I10 and the simplex circuit connected to the repeating coil I34, the monitor keys I93, I92 and their associated contacts, conductors I90 and I9I, test jacks 229, 223 and the contacts associated therewith, through the simplex connection on repeater 236, to line relay 200 in the radio station control circuit 300. Relay 206 operates, and at its contacts 20I completes a cirout to a hold relay 205 which is of a slow-torelease type. Relay 205 operates and at its contacts 206 completes an operating circuit from ground over conductor 3| 6 to transmitter con trol relay 320 and battery. Relay 265 at its contacts 251, prepares a self-holding circuit and a holding circuit for relay 2IIJ, and at its contacts 2B9 opens a point in the grid bias control circuit for tone detector circuit 293, to prevent operation of the detector circuit 293 responsive to impulses received over receiver 228 from a mobile unit 500. Relay 32f) operates and at its contacts 32I completes a circuit from the H5 volt 60 cycle supply 322 over master power switch 323 to the transmitter high voltage control circuit. In more detail the circuit may be traced over the right arm of switch 323, conductors 3 H, 345, 356, and 341, contacts 32I, conductor 328 to the primary of the transformer 3B2 feeding the high voltage rectifier circuit (not shown) of the radio transmitter 3M, and conductor 34!] back to the left hand side of the master switch 3223. Activation of the transmitter high voltage supply places the carrier of the transmitter 30I on the air in the conventional manner. Also, circuits in the transmitter, not shown, complete an operating circuit by way of conductors 334 and contacts 253 to relay 245. Relay 245 operates, and at its contacts 246 and 258, applies ground and battery through protective resistor 233, to a circuit including the primary windings of repeating coil 231, test jacks 22I and 222 and their associated contacts, conductors I54 and I95, jacks I96 and I91 and their 'associated contacts, through the hybrid circuit I83, conductors I89 and I89 and contacts I99 and I99 on the start key I98 to relay I86. Relay 2E5 further, at its contacts 241 and 249 opens the operating circuit for relay 240 temporarily.

The windings on relay I are arranged to aid each other when they are serially connected in a loop circuit to thereby cause operation of the relay, and to oppose each other whenever a parallel circuit is completed through them. Since the foregoing circuit from the contacts of relay 245 passes serially through the windings of relay I83, the latter relay operates. Relay III! in the trunk repeater 49 is also energized momentarily through relay I 30 by way of contacts I82 and conductor I13, but is made slightly slow-tooperate by the use of a small copper slug around the armature end of the core. Relay I 80 upon operating, opens its contacts I82, thereby opening the circuit of relay IIO before the latter can operate. Relay I89 also, at its contacts I 8I connects a characteristic dial tone on the calling line, by Way of conductor I12, as notice to the calling subscriber T that the control stations carrier is on the air, and that the dialing operation may be continued.

Responsive to transmission of the carrier wave by the radio transmitter 35 at the control station, circuits (not shown) associated with the radio receivers 460 in all of the mobile units, will cause operation of the associated squelch relay lIEI. Relay H0, at its contacts 4 closes the plate supply circuit to the pulse tone detector unit, comprising tubes 403 and 4M and their associated components. Contacts 4I2 and H4 of relay M0 at the same time apply holding ground to Various relay circuits of the mobile unit.

Selecting mobile unit The equipment is now conditioned for the subscriber T to select the desired mobile unit such as the unit 500, by a further dialing operation. Each of the mobile units has an assigned directory number and may be selectively signalled in a manner to be .set forth herein. Referring to Figure 4, the illustrated connections to the contact banks 404 and 465 are such that the illustrated mobile unit 1500 will be signalled responsive to the dialing of the digits 46.

Assuming that subscriber T wishes to establish a call to this illustrated mobile unit, he will now dial the digit 4 whereby the previously traced loop circuit which extends from subscriber substation T over trunk circuit 2, finder l0, selector H, and trunk circuit l2 to line relay in the trunk repeater 49 is opened and closed four times. Relay 60 (Fig. 1B) is released and energized four times in response thereto, and at its contacts 0| opens and closes the circuit extending over the signal-out conductor "0 and the connecting simplex circuit of repeating coils I04 and 236 .to pulsing relay 200. Relay 200 releases and energizes four times responsive to the impulses received over this circuit. Responsive to the open interval of the first impulse, relay 200 releases, and at its contacts 202, completes an operating circuit for relay 2H1, over a circuit including contacts 202, 208, and M9. Relay 2l0 operates, and at its contacts .2l2, completes a circuit from the secondary of transformer 281 of the pulse tone oscillator 289' to resistor 251. Resistor 251 is in series with the audio frequency input circuit which passes over conductors 306 and 301 to the transmitter 30!. This causes a 3000 cycle tone obtained from the dial tone oscillator arrangement 289 to be impressed upon the transmitter audio frequency input whereby it is further imposed upon the radio carrier by circuits therein .(not shown) as a 3000 cycle modulation of the carrier. Relay 2I0 also, at its contacts 2l3 complates a self-holding circuit over contacts 201,

M13 and 219 and at its contacts 2! prepares an operating circuit for relay 2I5. It is obvious that the radio station control circuit is transmitting .a .3000 cycle modulation on its carrier to represent th open period of a transmitted impulse. Responsive to the succeeding make period 'of the first impulse from the dial of subscriber T over the previously traced circuit, relay 200 re-energizes, and at its contacts 201 completes an energizing circuit for relay 2 l 5 over contacts 2 I 4. Relay 200 also, at its contacts 20! re-energizes relay 205, and at its contacts 202 opens the original operating circuit of relay 2l0. Relay 2l0 holds however, over a circuit including contacts H9, 213. and 201. Relay 205 remains operated for the series of impulses due to being of the slow-to-release type. Relay 2l5 operates and at its contacts 2H connects the secondary winding of the transformer 29l which is associated with the dial tone oscillator 290, to resistor 250. Resistor 258 is also connected to the audio frequency whereby a 2800 cycle tone obtained from the oscillator 200 is applied to the transmitter audio frequency input comprising conductors 306 and 301, by resistor 258. By means of conventional modulating equipment (not shown) in the transmitter .301, the transmitter carrier is modulated with 2.800 cycles by the radio transmitter to represent the. make period of a transmitted impulse. Relay H5, at its contacts 2l8 completes a self-holding circuit over the contacts 201, 2I8, and 2M, and at its contacts 2 l9 opens the holding circuit to relay 2). Relay 2l0 releases and at its contacts 212 disconnects the 3000 cycle modulation tone from the transmitter audio frequency imput, at its contacts 213 opens a further point in its self-holding circuit, and at its contacts 2M '14 opens the operating circuit to relay 2l 5. Relay -2l5 releases, at its contacts 2I1 disconnects the .2800 cycle modulation tone from the audio imput circuit for the transmitter, at its contacts 218 opens a further point in its holding circuit, and at its contacts 2l9 prepares the operating circuit for relay 2 l0 whereby the impulse relay arrangement comprising relays 200, 205, 2l0 and H5 is conditioned for receipt of a subsequent impulse. The impulse relay arrangement operates in a like manner for each of the four impulses received. It is obvious that each impulse received is transmitted over the radio carrier as a 3000- cycle tone and a 2800 cycle tone modulation of the carrier. It is important to note that relay 210 is shunted by resistance 225 which causes relay 2l0 to remain operated for a short interval of time after its holding circuit is interrupted by relay 2l5 at its contacts 2 I 9, whereby the carrier is modulated simultaneously for a brief interval of time by a combination of 3000 cycle and 2800 tones, for reasons to be more fully described at a later point herein.

The tone oscillator circuits 200 and 200 are of the conventional type, the oscillator 289 is effective to produce a 3000 cycle current in the secondary winding of its transformer 201, and the oscillator 290 is eifective to produce a 2800 cycle current in the secondary Winding of its transformer 29!. Each oscillator comprises, essentially, a conventional pentode tube arranged with a transformer and resistance and condenser elements, so as to produce the desired frequency in the'secondary winding of the transformer. In more detail, oscillator 209 comprises resistances 283 and 285 which are providedto reduce the effect of the grid of the pentode tube 288 as a load upon the tuned circuit 284' of the oscillator arrangement, whereby the frequency stability is improved in the event of operational changes in the field application. The condenser 284 bridges resistance 283 to increase the feedback voltage reaching the grid, the D. C. resistance of the grid circuit at the same time being maintained at as high a level as possible to keep the loading of the tuned circuit 284" light, for efficient stability control. Bias for the tube 288 is obtained from the drop across resistance 286 in the grid circuit. An obvious circuit exists from the plate to the transformer 281 whereby the 3000 cycle output of the pentode tube is impressed upon the primary winding of the transformer 281 and further induced into the secondary winding for the purpose above specified. The circuit for adjusting the output of the arrangement to the desired frequency comprises the transformer 281 and the condenser 284' the values of which may be changed to thereby change the frequency output. The oscillator 290 comprises elements similar to those contained in the oscillator 289, the values of the elements of the tuned circuits in this case being such as to produce the required 2800 cycle output.

Referring now to Fig. 4, the carrier, modulated with the two frequency tones is received by all of the antennas 400' associated with the receivers 400. The modulated currents thereupon are caused to appear across the audio frequency output of the receiver 400. This output circuit is connectedto the primary of the transformer H1 which further induces the tones into its secondary winding. The transformer secondary winding is connected over conductors 0.50 and 651, contacts 648 and 640, and conductors'654 and 665 to the tuned circuits 4| 8 and 9 of the mobile unit tone detector, which are further connected over conductor 658 and contacts 646, to ground. The tuned circuit 418 comprises transformer 40! and condenser 49| in arranged relation whereby they are efi'ective to select the incoming 3000 cycle tone and apply it to thegrid of tube 403. Tube 403 is operated with its grid biased negative close to cutoff so that when the tone selected by the associated tuned circuit 4| 8 appears on the grid of the tube, the tube will conduct. The tuned circuit 4l9, comprising transformer 402' and condenser 402 is tuned to a frequency of 2800 cycles and is effective to select the incoming 2800 cycle tone and apply it to the grid of tube 404. Inasmuch as the 3000 cycle frequency is received first from the transmitting source at the fixed control station, the tube 403 conducts first, and causes operation of relay 445 which is connected in the plate circuit of tube 403 over conductor 066, contacts 642, conductor 6', through relay 445 and resistance bank 445, to the cathode of tube 453. When the 2800 cycle tone is received from the control station transmitter SDI, just prior to termination of the 3000 cycle tone the 2800 cycle tone is induced into the secondary of the transformer 4|! and thus into the tuned circuits 45S and 4I9 over the previously traced circuit to ground at contacts 646. The tuned circuit M9 is now eifective to select the 2800 cycle tone and impress it upon the grid of tube 404. Tube 404 is also normally provided with a negative grid bias close to cutoff, so that when the tone selected by tuned circuit 4l9 appears on the grid of tube 404, the tube conducts, and effects operation of relay 440 which is located in the plate circuit of tube 404. This circuit extends from the plate of tube 404 over conductor 651, contacts 644, conductor 610, relay 440 and through the resistance network 443 to the cathode of tube 464.

Relay 445 operates responsive to tube 403 being rendered conductive, and at its contacts 446 completes an operating circuit for relay 450 extending from contacts 4! of the operated squelch relay 4l0, over contacts 425, conductor 431, and contacts 446, Ml, to relay 455. Relay 450 operates, and at its contacts 45| completes an operating circuit for hold relay 455. Relay 450 also, at its contacts 452 prepares a circuit to the motor magnet 459 of the rotary switch 444 and at its contacts 453 completes a condenser short-circuit for its own winding whereby it will be slow to release. Hold relay 455 operates, at its contacts 450 completes a circuit to the rotary switch release magnet 450, and at its contacts 45'! opens a point in the circuit to the contact banks 464 and 465. Release magnet 458 operates to engage the holding pawl of the rotary switch. Rotary switch 444 is a small ratchet drive stepping switch having a pair of contact banks 464 and 465, each contact bank having 10 contacts. A holding pawl (not shown) having two positions, is regulated to each of these positions by the release magnet 458. When the release magnet 458 is energized, the holding pawl engages the ratchet to hold the wipers at the point to which they have been operated. Upon deenergization of the release magnet, the holding pawl is disengaged and the switch wipers restore to their normal position under spring tension.

When the second modulation of the carrier is received to operate tube 404 and its associated relay 440 in the manner'described heretofore, relay 440 operates, and at its contacts MI and 442 opens the operating circuit to relay 450, and completes an operating circuit to the operating magnet 459 of the rotary switch 444. The operating circuit for magnet 459 extends over contacts M2, 426, conductor 43?, contacts 446, 442, 452 to the magnet 459. Motor magnet 459 operates to cause the wipers 464 and 465 to advance one step clockwise in the banks 464 and 465 in a well known manner. Inasmuch as the release magnet 458 is operated, the holding pawl of the rotary switch will engage the ratchet to hold the wipers on the first contact.

It should be noted that the circuit to the motor magnet 459 of the rotary switch will be completed only if relays 440, 445 and 450 are operated. Further, the circuit will be completed only momentarily in that the operating circuit to relay 450 is opened at contacts 44| whenever relay 440 is operated, thereby effecting release of relay 450 and consequent interruption of the aforetraced operating circuit. Since the circuit is completed only when relay 440 is operated, it is obvious that the momentary pulse to motor magnet 459 will have a time duration equivalent to the release period of relay 450, as determined by the discharge time of condenser 453'. The purpose of transmitting two successive tones per pulse to operate two relays in a definite sequence is to reduce dialling interference, and to prevent needless operation of the rotary switch. For example, whenever a crash of static is received by the receiver 400, the resultant transient currents in each of the tuned circuits would appear simultaneously upon the grids of the tubes 403 and 404 to render these conductive. Relays 440 and 445 would thereupon operate simultaneously and continue in operation for the interval of time that the interference was effective. However, inasmuch as relay 440 is arranged at its contacts 44! to open the circuit to relay 450, relay 450 can not operate whenever the relays 440 and 445 are initially simultaneously operated, and the motor magnet of the rotary switch will not receive a false impulse.

The release magnet 458 will remain operated for the series of impulses comprising a received digit inasmuch as hold relay 455 remains operated due to being of a slow to release nature. The relays 440 and 445 release upon removal of the tones at the end of each pulse, and re-operate as described to re-operate relay 450 at each succeeding impulse. Relay 450, at each energization, will complete the operating circuit to motor magnet 459 to cause the rotary switch to advance one step for each impulse. Therefore, it is obvious that the wipers 464' and 465 will be stepped to the fourth contact of banks 454 and 465 responsive to the digit 4 which has been dialled by subscriber T. When the'wipers reach the fourth contact, they are retained in this position by the holding pawl, which is controlled by the operated release magnet 450 as heretofore mentioned. After a short interval of time following the receipt of the last impulse of the series comprising the transmitted digit 4 and the final release of relay 450, the slow-releasing hold relay 455 also restores. Relay 455, at its contacts 451, which are arranged to make prior to the break of its contacts 456, completes a circuit from ground over contacts M2, 426, conductor 437, contacts 45?, 45!, wiper 454' and the 4th contact of bank 464 to relay 460. Hold relay 455 next opens its contacts 455 to eifect deener- 17 gization of release magnet 458. When release magnet 458 de'energizes, the holding pawl is disengaged and the rotary switch is returned by mechanical spring action (not shown) to its normal position. Relay 460 operates responsive to the temporary ground received over the previously traced circuit, and at its make first contacts 463 completes a self-holding circuit over contacts 412 of the operated squelch relay 410, contacts 426, conductor 431, and contacts 463. Relay 460 also, at its contacts 461 opens a portion of its operating circuit, at its contacts 452 prepares an operating circuit for relay 411].

When the succeeding digit 6 is dialled by the subscriber T, the equipment in the automatic exchange is effective to repeat the digit comprising 6 impulses to the control station. The equipment therein in turn, causes 6 modulated impulses to be transmitted over the carrier to the mobile units. These incoming impulses are received by the radio receiver 400 and are converted similarly into direct current pulses for the operation of motor magnet 459 of the rotary switch, by the pulsing relays 4411, 445, 450, 455. The wipers of the rotary switch are thereupon, stepped to the sixth contact of the wiper banks 464 and 4155. Shortly after termination of the sixth impulse hold relay 455 releases, as before. Relay 455, at its make first contacts 451, completes a circuit over contacts 412, 425, conductor 431, contacts 451, 462, wiper 465' and the 6th contact of bank 465 to relay 411i. Relay 455, at its contacts 456, then opens the circuit to release magnet 458, which deenergizes and disengages the holding pawl for the rotary switch, to effect release of the rotary switch to its normal position. Relay 41!! operates, and at its make first contacts 411, completes a self-holding circuit over contacts 412, conductor 492, and contacts 411. Relay 415 at its contacts 412, completes a circuit to light the incoming call lamp 514 over conductor '20, switch 518, and conductor 525, as a visual indication to the subscriber in the mobile unit that there is an incoming call awaiting his answer. Relay 410 also, at its contacts 413 and 415, completes a circuit from the vibratory side of the high voltage rectifier unit (not shown) of the receiver 4130, over conductor 4%, contacts 421, conductor 490, contacts 415 and conductor 491 to the input circuit of the output amplifier stage (not shown) of the receiver 448, which delivers the tone amplified back through the amplifier output leads of the receiver over conductor 489, contacts 413, conductor 522 to the handset receiver connection, as an audible signal to the mobile suuscriber. This signal, which is applied to the handset receiver, is a tone of very high level, said signal being merely one form of signal that may be utilized for such purpose.

Mobile subscriber answers Responsive to the audible and visual signals received by the subscriber located in the mobile unit 5130 which has been selectively seized by subscriber T, the called subscriber lifts his handset 501 from hook 503 whereby a circuit is completed to relay 429 over contacts 412, conductor 452, contacts 415, conductor 523, contacts 584, conductor 528, contacts 144, and 134, and conductor 101 to relay 428. A branch of this circuit also extends through contacts 133 to the motor 115 of the call timer to start operation thereof. At the same time, contacts 5% close a direct circuit over conductor 529 to clutch magnet 115. Clutch magnet 116 is thereby energized the operating circuit for relay 245.

and connects the motor and reduction gear unit to the shaft which mounts cams 120 and 131] whereby the said cams are driven in a clockwise direction at a rate of speed approximating one revolution in five minutes. In addition to the foregoing, the removal of the handset 501 also lights the in use lamp 515 on the dash, over contacts 504 and 505.

Relay 42!! operates, and at its contacts 421, completes a circuit for power relay 630 over contacts 412, 421, and conductor 554. Relay 420 also, at its contacts 422 disconnects the audio frequency output circuit of radio receiver 400 from the transformer 411 leading to the pulse detecting circuit, and connects the said audio frequency output of the receiver 400 over contacts 423, conductor 522, to the handset receiver circuit. Relay 421) at its contacts 424, opens the plate'supply to the tone detector vacuum tubes'41l3 and 4114 thereby preventing any possible operation of the impulse responsive equipment as a result of incoming transient tones. Relay 428 at its contacts 42'6, opens the holding circuit for relay 460, and at its contacts 421 opens the tone signal circuit to thereby terminate the audible signal to the mobile subscriber. At its contacts 423 relay 42B completes a self holding circuit over contacts 412, contacts 428, conductor 523, contacts 5134, conductor 526, contacts 1114 and 134 and conductor 101.

Relay 634 operates and at its contacts 631, completes an operating circuit for the dynamotor equipment 1550 to thereby supply the radio transmitter 603 with the high voltage necessary for generation of the transmitters carrier. At the same time, direct currentis supplied to the handset transmitter circuit from battery through relay 631], over conductor 632, induction coil 633, the primary-of transformer coil 651 and conductor 512 and the handset transmitter to conductor 528 and ground. The outgoing speech circuit now comprises the handset 5131, conductor 612, the primary of transformer 551 and condenser 634. The outgoing speech is thus induced into the transformer secondary which is connected to the radio transmitter modulation circuit. The mobile units carrier is placed on the air responsive'to operation of the dynamotor 650 and the consequent energization of the high voltage supply circuit for the transmitter. I

In the fixed radio station control circuit, radio receiver 228 intercepts the transmitted mobileunit carrier and squelch relay 25B is operated therefrom over conductors 229 responsive to receipt of this carrier. Relay 25!] upon operating its contacts 251 completes a multiple operating circuit for relay 320, and at its contacts 253 opens Relay 245 thereupon restores, at its contacts 243 and 248 opens the operating circuit for relay 180, and at its contacts 241 and 249 prepares an operating circuit for signal-in relay 110 (Fig. 1B). Relay releases, removes dial tone, and at its contacts 182 completes a circuit for signal-in relay 11%) over the simplex circuit comprising contacts 254, 282, 213, contacts 244and 242, both windings of relay 246 in parallel, contacts 249 and 241, both secondary windings of repeating coil 231, the contacts of monitor jacks 221 and 222, conductors 195 and 194, contacts of jacks 193 and 191, lower windings of repeating coil 183, conductors 139 and 183, contacts of key 198, both windings of relay 185 in parallel, contacts 182, and conductor 113 to relay 1113. Relays'240 and 134 will not operate'in this circuit due to their windings being energized in' opposition, but rel'ay II9 operates, and completes, at contacts H3, a circuit for'operating hold relay I59.

- Upon operating, the hold relay I59 completes at contacts I52 a circuit for operating the slow to operate relay I49 from contacts I92. Upon operating, relay I49"completes, at' contacts I45, a secondary holding circuit including contacts I61 for maintaining operated the holdrelay I59. Eurther, relay I49 completes at contacts I44 a circuit including contacts II3 for operating reverse battery relay 59. Upon operating, the reverse battery relay 59 reverses at contacts 52, 53 and 54 polarity of the outgoing trunk I2 with respect to the line relay 99, which reversal of polarity may be utilized in the finder-selector line illustrated and included in the loop circuit extending: to the calling subscriber substation T for metering or supervisory purposes.

At this time a talking connection has been completed from the calling subscriber T over the automatic exchange I', the repeater. 49, the central office auxiliary equipment I19, radio station control circuit 399, to the mobile unit set 599. The outward talking circuit extends from subscriber sub-station T over conductors 3 and' 4, finder I9, selector II, conductors l4, I5 of trunk circuit I2, contacts 5I and 53, 93 and 95, conductors HI and I12, repeating coil I83, trunk circuit I85, repeating coil I 84, monitor jacks .I92 and I93, conductors I99 and I9I, monitor jacks 229=and 223, repeating coil 236, through the low pass filter 295, and conductors 393 and 391- to the audio frequency input to transmitter 39I, whereby the audio frequencies are impressed upon'the carrier and transmitted to the radio receiver: 499 in the mobile unit set 599, and whence they appear across the audio frequency output andthence over contacts 423', and conductor 522 to the receiver of the handset 59L Speech impressed HD0111 the transmitter of the handset 59I by'the called subscriber is transmitted over. conductor 612, to the primary winding of transformer 65I, from which it is induced into the secondary of transformer 65I and to the audio frequency input of radio transmitter 699, from whence it is superimposed upon the transmitter carrier and enters the air over antenna 699'. Radio receiver 228 located in radio station control circuit 399 receives the incoming modulated carrier and impresses the voice currents on the conductors 233, which are connected to the primary winding of transformer 231, whereupon the voice signals are inducted into the secondary of transformer'231 and extended over monitor lacks 22I, 222, conductors I94 and I95, jacks I96 and I91. to the hybridrepeat-ing coil I83, whereupon they are induced'into the upper winding-sci the hybrid coil and transmitted over conductors HI and I12, contacts 93 and 95, contacts 53 and 5!, conductors I4 and I5 of trunk circuit I2, selector II, finder I9, conductors 3 and 4 of the line 2 to the substation T.

Normal release At the conclusion of the conversation, assuming that the subscriber at the calling subscriber sub-station T in the automatic exchange I replaces the receiver of his telephone instrument first, the loop circuit extending between the calling subscriber sub-station T and the line relay 69 in the trunk circuit I2 is interrupted, causing the latter relay to restore. Uponrestoring, the line-relay 99 completes, at contacts 62., the previously; traced terminationcircuit including resis-tor I14, contacts WI, 62, condenser I15, across line conductors HI and I12, which extendbetween the trunk circuit I2 and the hybridv coil I83 and the balancing network I89 in the central oflice auxiliary equipment I19. Also the line relay 69 interrupts, at contacts 6| the previously traced circuit to the signal-out conduct-0r I19, to thereby bring'about restoration of pulsing relay 299 in the radio station control circuit and the consequent release of relay 295 shortly there'- after. Relay 295 in releasing opens one of the holding circuits for relay 329 at its contacts 296. However, relay 329 is held operated over contacts 25I on squelch relay 259, which is kept operated by them-obile units carrier.

When the called subscriber at the mobile set 599 replaces the handset Bill on its associated switch hook 593, the previously mentioned circuits for holding relay 429 and the timer operated are interrupted, at contacts 594 and 59.9. Relay 429 thereupon restores, at its contacts 42I opens the operating circuit for relay 939, at its contacts 423' opens the connection from the audio frequency output of radio receiver 499 to the handset 59I, at its contacts 422 reconnects the audio frequency output to the transformer M1 in the tone detector input circuit, and at its contacts 424 reconnects battery supply to the plate circuit in the vacuum tubes 493 and 494 of the tone detector. The timer motor is thereby stopped and the clutch 1| 6 disengaged. Return spring 1IB thereupon returns the cams 129 and 139 to the normal, illustrated position. Relay 639 releases, wherebythe high voltage supply to radio transmitter 699 is opened and the mobile units carrier ceases to be transmitted by radio transmitter 599.

squelch relay" 2'59 associated with radio receiver 228 in the radio station control circuit 399 releases, responsive to removal of the mobile unit's carrier from the air, and at its contacts 251 opens-the operating circuit for-power relay 329. Relay 329 then releases, and at its contacts 32I opens the supply circuit for the high voltage rectifier circuit of the transmitter 39I to thereby remove the fixed stations carrier from the air. Relay 259 also, at its contacts 254, opens the operating circuit for relay I I9. Relay II 9 releases and at its contacts I I3, opens the holding circuits for relays I59 and 59. Relay 59 restores immediately and the hold relay I59 restores shortly thereafter, it being of the slow to release type, due to having a copper sleeve over its core. Upon restoring, the reverse battery re lay 59 re-establi'shes at contacts 5|, 52, 53 and 54, the normal polarity of the outgoin trunk I2 with respect to the line relay 69 in the trunk circuit. The hold relay I 59 upon restoring, interrupts, at contacts I52, the holding circuit for the relay I49. Relay I49 then restores and interrupts at contacts I45, the previously traced circuit for holding relay I99 operated, whereby the latter relay also releases, after a short delay, it being likewise of the slow to release type. Hold relay I69 upon restoring, at con-tacts I66 remove-s ground from test conductor I6, and recompletes, at its contacts I95, the circuit for applying battery potential by way of impedance 19, contacts 91, I65, to the said test conductor I5 of outgoing trunk I2. When ground potential is removed from the control or test conductor I9 of the outgoing trunk I2, the selector II and finder I9 are released, and the application of battery potential to the control conductor l6 marks the outgoing trunk I2 as idle to the outgoing selectors 

